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[vsnet-alert 830] CVC 132 (DV UMa, V795 Cyg, SX LMi, AQ CMi)

BELGIAN ASTRONOMICAL SOCIETY V.V.S. -  Working Group Variable Stars
Cataclysmic Variables Circular No.132                1997, April 08
Ed.: T. Vanmunster, Walhostraat 1A, 3401 Landen, BELGIUM
     Internet: tvanmuns@innet.be                  TEL. 32-11-831504
     CBA Belgium Web Page : http://vsnet.astro.columbia.edu/~cba/be
===================================================================

DV UMa [UGSU, 15.4v - 20.6v]
============================

Timo Kinnunen, Finland and Tonny Vanmunster, Belgium independently 
report a visual outburst detection of this most interesting dwarf 
nova (part of the TA/BAA VSS Recurrent Objects programme). The 
available observations are :

1997 Apr 07.877 UT, <15.2  (G. Poyner, visual);
     Apr 07.890 UT, <14.8  (T. Vanmunster, visual);
     Apr 08.85  UT,  13.9  (T. Kinnunen, visual);
     Apr 08.931 UT,  14.0  (T. Vanmunster);

DV UMa was last seen in outburst on Feb 26, 1995 by Vanmunster [CVC 28].
During that outburst, time-series photometry by the Ouda team at Kyoto
University, Japan revealed superhumps with a period of 0.08585 +/- 
0.00001 day, a value that is significantly different from the published 
Porb (0.08579 day). [CVC 29]. Accurate astrometry by Nick James, Chelmsford, 
UK gave following position of DV UMa : RA = 9h46m36s.64, decl = +44g46'44".8 
(J2000.0). This is 2" W and 4" N of the position in 'A Catalog and Atlas 
of Cataclysmic Variables' [Downes, R.A., Shara, M.M., 1993, PASP, 105, 
127-245].

DV UMa was discovered by Usher et al. (1981) as an ultraviolet excess
object. The object was subsequently identified as an eclipsing cataclysmic
variable by Howell et al. (1988).  Their photometric observations showed
deep eclipses (1.5 mag or more) with an orbital period of 0.08597 day.
Eclipses lasted about 0.15 Porb ~ slightly shorter than 20 min.


V795 Cyg [UGSS, 13.4p - <17.9:p]
================================

Lasse Jensen, Denmark and Patrick Schmeer independently detected
an outburst of V795 Cyg, which is part of the TA/BAA VSS Recurrent
Objects Programme. Several confirmative observations have been
received.

1997 Apr 07.010 UT, 13.0:  (P. Schmeer, visual);
     Apr 07.082 IT, 13.4   (L. Jensen, unfiltered CCD);
     Apr 07.142 UT, 12.7   (P. Schmeer);
     Apr 08.037 UT, 12.7   (B. Worraker, visual);
     Apr 08.05  UT, 12.7   (T. Kinnunen, visual);
     Apr 08.082 UT, 12.6   (G. Poyner, visual);
     Apr 08.09  UT, 13.1   (T. Vanmunster, CCD); 

V795 Cyg was last reported in outburst on May 2, 1995 by Vammunster
and Jensen [CVC 36].

The present classification of V795 Cyg as a SS Cyg type dwarf nova
is partially based on the apparent absence of superhumps in a
1.5 hour CCD photometry run by T. Kato during the November 1992
outburst of V795 Cyg.


SX LMi [UGSU, 16B]
==================

The SX LMi outburst, announced in our previous circular, is a 
superoutburst. Unfiltered time-series photometry at CBA Belgium 
Observatory, using a 0.25-m SCT and ST-7 CCD, on April 7/8
1997 clearly shows the presence of superhumps. A very preliminary
analysis of the superhump period yields a best value of approx.
101 min (PDM method) and a mean amplitude of ~ 0.1 mag. 
CCD photometry at CBA Belgium Observatory on the night before
(April 6/7 1997) did not reveal any superhumps, but clearly showed
small-amplitude (semi-)periodic oscillations, which very likely
are to be interpreted as emerging superhumps.

A further comment on the superhump and orbital period of SX LMi was 
sent to us by John Thorstensen, Dartmouth College : "There's a paper 
in press by Wagner et al. -- I'm a co-author -- which gives 
P-orb = 0.06717 +- 1.1 x 10^-4 d, or 96.72 +- 0.16 min, and a 
superhump period of 0.06893 +- 0.00012 d.  The Porb is from spectro-
scopy during quiescence ... and the P-superhump is from a few nights 
of photometry during the 1994 outburst."

Since there is still a slight possibility of a cycle-count error, 
follow-up time-series photometry on successive nights and at various
longitudes would be of much value.


Further observations of the present outburst :

-------------------------------------------
DATE (UT)       MAGN   MS  OBSERVER   
-------------------------------------------
1997 03 26.933   15.2: mv  Poyner
1997 03 27.021   15.4: mv  Poyner
1997 03 28.967  <15.5  mv  Poyner
1997 04 02.89   <15.6  mv  Kinnunen
1997 04 06.82    13.3  mv  Kinnunen
1997 04 06.82    13.6  mv  Pietz
1997 04 06.898   13.4  mv  Vanmunster
1997 04 06.913   13.9  mv  Broens
1997 04 07.82    13.2  mv  Kinnunen
1997 04 07.874   13.2  mv  Poyner
1997 04 07.892   13.1  mv  Worraker
1997 04 07.964   13.3  mv  Poyner
1997 04 07.970   13.1  mv  Worraker
1997 04 07.997   13.1  mv  Worraker
1997 04 08.041   13.1  mv  Worraker
1997 04 08.06    13.5  mv  Kinnunen
1997 04 08.083   13.2  mv  Poyner



AQ CMi [UGSU, 14.5p - <16.5p]
=============================

Nick James, UK reports some follow-up observations of this interesting
object : "I obtained a further image of the AQ CMi field in V-Band last 
night (April 6, 1997) but the star was not seen to an estimated limiting 
magnitude of 17.5V. The VSNET star at V17.47 is clearly seen. The latest 
images are:

April 3.886 (15.5V)   http://vsnet.astro1.demon.co.uk/images/aqcmi_970403.jpg
April 6.865 ([17.5V)  http://vsnet.astro1.demon.co.uk/images/aqcmi_970406.jpg "


Tonny Vanmunster

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